1. Field of the Invention
This invention relates to a novel membrane apparatus design. The apparatus is useful in producing permeable membrane elements for use in separating mixtures into various components under various separation conditions such as reverse osmosis, ultrafiltration dialysis, pervaporation or perstraction conditions. The design facilitates fabrication of membrane elements without the use of adhesives for use in the processing of viscous systems, especially of mixtures of organic liquids, at elevated temperatures and/or pressures or under vacuum (as in pervaporation).
2. Prior Art
Semipermeable membrane elements for industrial uses can be assembled in four different configurations: plate and frame (P and F), tubular (T), spiral wound (SW) and hollow fiber (HF). Most commercial units today utilize spiral wound or hollow fiber configurations which provide large membrane packing density (surface area per unit volume). The plate and frame and tubular designs have lower packing densities and are, therefore, used in special applications. The hollow fiber design has very high packing density but may be limited by high pressure drops and uneven flow distribution.
These systems have operating pressure limitations. For example, spiral wound and hollow fiber designs can be operated at about 500-1000 psig pressure in reverse osmosis applications and at lower pressures (50-100 psig) in ultrafiltration applications, while the tubular and plate and frame designs are normally limited to 10-100 psig operating pressures.
The standard spiral wound design is suitable for many applications but requires the use of an adhesive. Because adhesives are relied upon to make the numerous membrane-to-membrane and membrane-to-permeate tube seals, it is very important to maintain strong bond throughout the element's life. If seals weaken, leakage occurs and the element fails.
As many adhesives soften (swell) or dissolve in organic liquids, particularly at high temperatures, it is desirable to minimize or eliminate their use in designs of units to be used for organic systems. Some references briefly disclose means to avoid the use of glue by clamping devices, pressure plates, etc. These include U.S. Pat. No. 4,019,988, U.S. Pat. No. 4,009,107; U.S. Pat. No. 3,768,660; U.S. Pat. No. 3,786,925, U.S. Pat. No. 3,705,652, U.S. Pat. No. 3,979,297, U.S. Pat. No. 3,397,790, U.S. Pat. No. 3,367,504, U.S. Pat. No. 3,417,870, and U.S. Pat. No. 4,009,108.
In addition to the four main designs described above there are several other membrane element designs which have been described in the art and are extensively used, especially in dialysis and hemodialysis. For example, U.S. Pat. No. 3,701,431 describes such a design which can be operated at high pressure and in which membrane sheets are clamped together with an interposed spacer sheet to form a tube. Multiple tubes can be arranged to form the element.
Japanese Patent No. J79035-194 describes an osmotic filtration membrane device comprising a flattened semipermeable membrane tube with a flat-plate spacer located in the tube. The tube is corrugated with a number of spacers, each being disposed between the adjacent turns of the corrugated tube. The liquid enters into the tube and the filtered liquid discharges from the hollow space between the tube turns.
German Patent No. DE 3028-398 discloses an ultrafiltration unit for biological fluids which has rectangular semipermeable membranes stacked in pairs with spacers, in which the edges are sealed by embedding in a cured resin, such as epoxy. The stack is covered with a pressure plate to maintain proper spacing.
German Patent No. De 3141388 discloses an ultrafiltration unit being a small sterile filtration unit for medicine or laboratory use, having microporous bags with open ends fixed in a plastic disk.
GB Pat. No. 2,001,867 describes a disposable hemodialyzer with flattened membrane tubes in which blood passes successively over two groups of tubes which are stacked in parallel within a housing in which the ends of the tubes are embedded in cured plastic. This design is suitable for dialysis having a pressure limitation fixed by the dialysis mechanism of 15 psi.
The following references also disclose similar dialysis devices: Defensive Publication No. T867005; U.S. Pat. No. 3,522,885, U.S. Pat. No. 3,565,258, U.S. Pat. No. 4,128,479, U.S. Pat. No. 3,864,265, U.S. Pat. No. 4,066,553, and U.S. Pat. No. 4,163,721.
What is desired is a membrane apparatus possessing three main characteristics: (1) suitability for use with organic systems which may also be viscous over a wide range of operating temperatures, (2) large membrane packing density, and (3) and will operate at high pressures. Specifically desired in an apparatus which will operate in the pressure range required for ultrafiltration and reverse osmosis, about 10-1000 psig and will operate at a range of temperatures from about 20.degree. C. to 200.degree. C. and higher, in the presence of organic systems that may have a viscosity an order of magnitude higher than that of water.